Such a nozzle stage is described in document FR 2 922 950 in the name of the Applicant, and it comprises two coaxial shrouds, a radially inner shroud and a radially outer shroud, together with radial vanes extending between the shrouds and connected via their ends to the shrouds, and also a support for abradable material that is mounted by crimping to the upstream and downstream edges of the inner shroud.
In known manner, the inner shroud presents openings having the radially inner ends of the vanes inserted and fastened therein.
More precisely, the radially inner ends of the vanes include tenons that project along the axes of the vanes. The shroud is made of two superposed annular sheets, an outer sheet and an inner sheet, that are fastened together by brazing, the outer sheet presenting openings in which the radially inner ends of the vanes are mounted, the inner sheet presenting openings for receiving the above-mentioned tenons, and being crimped via their upstream and downstream edges onto the support for abradable material.
The radially inner ends of the vanes thus bear radially against the inner annular sheet, and they are also held axially by the tenons that are engaged in the openings in the inner annular sheet. The radially inner ends of the vanes are fastened by brazing to the annular sheets.
Such a structure presents the drawbacks set out below.
Firstly, the crimping of the abradable support to the inner shroud is performed by folding the upstream and downstream edges of the inner annular sheet, thereby damaging the brazing between the two annular sheets at said edges. The outer annular sheet may separate a little from the inner annular sheet, in particular at the upstream edge, thereby requiring manual re-touching at the end of fabrication, or else a maintenance operation when the separation is detected during a subsequent maintenance inspection.
Furthermore, the inner annular sheet is stressed simultaneously by the crimping of its upstream and downstream edges, by the brazing of the tenons of the vanes, and by the brazing of the outer annular sheet. This requires the shape of the inner sheet to be under perfect control, since it is taken to its capacity limit for shaping.
Finally, such a structure makes it necessary simultaneously to make openings through the inner sheet and openings through the outer sheet, and to use vanes that are complex in structure, presenting tenons at their radially inner ends, in order to retain the vanes radially.